1. Field of the Invention
This invention relates to a method for cultivating floating animal cells in a cell culture unit composed of hollow fibers. More particularly it is concerned with a method for cultivating floating animal cells in a cell culture unit composed of a shell and open ended hollow fibers enclosed in the shell, comprising introducing a culture medium through the hollow fibers and cultivating the floating animal cells in the space between the shell and the hollow fibers. The present invention also relates to a floating animal cell culture unit used for the method.
2. Description of the Prior Art
Various methods for cultivating animal cells have been known. Animal cells include those which grow and proliferate while attached to a growth surface (referred to as "attaching cells") and those which grow and proliferate in a floating state (referred to as "floating cells"). Significant advances have been made in the study of cultivation of attaching cells.
Such attaching cells can generally grow and proliferate only in a single layer on the attached surface. Richard A. Knazek, et al., however, have succeeded in three-dimensionally growing and proliferating attaching cells by employing a method in which the attaching cells are grown on the exterior surface of semipermeable hollow fibers or capillaries and a culture medium is passed through the hollow fibers or capillaries (see Journal of Medicine, Vol. 296, No. 3, pp. 154-159 (1977)). Additionally, U.S. Pat. No. 3,997,396 discloses a method of three-dimensionally growing and proliferating attaching cells in which the attaching cells are grown on one surface of a hollow fiber membrane and oxygen is supplied to the other surface.
Floating cells are generally weak as compared with attaching cells (see Shoichi Oboshi et al., Jingansaibo no Baiyo, Asakura Shoten, Tokyo, page 44 (1975)). It has therefore been considered difficult to grow and proliferate the floating cells in desired high densities. Such considerations have led to the conclusion that all of the above-described methods using hollow fibers are limited to the cultivation of the attaching cells.
Methods which are generally used in the cultivation of floating cells include a stationary floating culture method and a suspension culture method using agitation, rotary stirring, or the like. These methods, however, have disadvantages, in that: (1) large scale equipment is required, since it is difficult to grow and proliferate the cells in high densities; (2) difficulties are encountered in separating the cells from nutrients, metabolic products, wastes, etc.; (3) it is difficult to continuously exchange the culture medium; and (4) the possibility of being contaminated by other microorganisms is great. It has, therefore, been greatly desired to remove these disadvantages, in particular, on the ground that the floating cells produce metabolic products which are of importance from the medical and veterinary standpoint, e.g., diagnosis and medical treatment of various diseases.
As described above, the progress in the method of growing and proliferating attaching animal cells is remarkable, and it has now become possible to grow and proliferate the attaching animal cells three-dimensionally, i.e., like a tissue, by using hollow fibers. On the other hand, the cultivation of the floating cells has been carried out by the conventional methods as described above. According to these methods, it is difficult to grow and proliferate floating cells in high densities. Therefore, various problems are involved in producing useful metabolic products from the floating cells by the cultivation thereof in large amounts.